Add a reset driver framework/uclass

A reset controller is a hardware module that controls reset signals that
affect other hardware modules or chips.

This patch defines a standard API that connects reset clients (i.e. the
drivers for devices affected by reset signals) to drivers for reset
controllers/providers. Initially, DT is the only supported method for
connecting the two.

The DT binding specification (reset.txt) was taken from Linux kernel
v4.5's Documentation/devicetree/bindings/reset/reset.txt.

Signed-off-by: Stephen Warren <swarren@nvidia.com>
Acked-by: Simon Glass <sjg@chromium.org>

drivers/Kconfig

@@ -56,6 +56,8 @@ source "drivers/ram/Kconfig"
 
 source "drivers/remoteproc/Kconfig"
 
+source "drivers/reset/Kconfig"
+
 source "drivers/rtc/Kconfig"
 
 source "drivers/serial/Kconfig"

drivers/Makefile

@@ -68,6 +68,7 @@ obj-$(CONFIG_U_QE) += qe/
 obj-y += mailbox/
 obj-y += memory/
 obj-y += pwm/
+obj-y += reset/
 obj-y += input/
 # SOC specific infrastructure drivers.
 obj-y += soc/

drivers/reset/Kconfig

@@ -0,0 +1,15 @@
+menu "Reset Controller Support"
+
+config DM_RESET
+	bool "Enable reset controllers using Driver Model"
+	depends on DM && OF_CONTROL
+	help
+	  Enable support for the reset controller driver class. Many hardware
+	  modules are equipped with a reset signal, typically driven by some
+	  reset controller hardware module within the chip. In U-Boot, reset
+	  controller drivers allow control over these reset signals. In some
+	  cases this API is applicable to chips outside the CPU as well,
+	  although driving such reset isgnals using GPIOs may be more
+	  appropriate in this case.
+
+endmenu

drivers/reset/Makefile

@@ -0,0 +1,5 @@
+# Copyright (c) 2016, NVIDIA CORPORATION.
+#
+# SPDX-License-Identifier: GPL-2.0
+
+obj-$(CONFIG_DM_RESET) += reset-uclass.o

drivers/reset/reset-uclass.c

@@ -0,0 +1,131 @@
+/*
+ * Copyright (c) 2016, NVIDIA CORPORATION.
+ *
+ * SPDX-License-Identifier: GPL-2.0
+ */
+
+#include <common.h>
+#include <dm.h>
+#include <fdtdec.h>
+#include <reset.h>
+#include <reset-uclass.h>
+
+DECLARE_GLOBAL_DATA_PTR;
+
+static inline struct reset_ops *reset_dev_ops(struct udevice *dev)
+{
+	return (struct reset_ops *)dev->driver->ops;
+}
+
+static int reset_of_xlate_default(struct reset_ctl *reset_ctl,
+				  struct fdtdec_phandle_args *args)
+{
+	debug("%s(reset_ctl=%p)\n", __func__, reset_ctl);
+
+	if (args->args_count != 1) {
+		debug("Invaild args_count: %d\n", args->args_count);
+		return -EINVAL;
+	}
+
+	reset_ctl->id = args->args[0];
+
+	return 0;
+}
+
+int reset_get_by_index(struct udevice *dev, int index,
+		       struct reset_ctl *reset_ctl)
+{
+	struct fdtdec_phandle_args args;
+	int ret;
+	struct udevice *dev_reset;
+	struct reset_ops *ops;
+
+	debug("%s(dev=%p, index=%d, reset_ctl=%p)\n", __func__, dev, index,
+	      reset_ctl);
+
+	ret = fdtdec_parse_phandle_with_args(gd->fdt_blob, dev->of_offset,
+					     "resets", "#reset-cells", 0,
+					     index, &args);
+	if (ret) {
+		debug("%s: fdtdec_parse_phandle_with_args failed: %d\n",
+		      __func__, ret);
+		return ret;
+	}
+
+	ret = uclass_get_device_by_of_offset(UCLASS_RESET, args.node,
+					     &dev_reset);
+	if (ret) {
+		debug("%s: uclass_get_device_by_of_offset failed: %d\n",
+		      __func__, ret);
+		return ret;
+	}
+	ops = reset_dev_ops(dev_reset);
+
+	reset_ctl->dev = dev_reset;
+	if (ops->of_xlate)
+		ret = ops->of_xlate(reset_ctl, &args);
+	else
+		ret = reset_of_xlate_default(reset_ctl, &args);
+	if (ret) {
+		debug("of_xlate() failed: %d\n", ret);
+		return ret;
+	}
+
+	ret = ops->request(reset_ctl);
+	if (ret) {
+		debug("ops->request() failed: %d\n", ret);
+		return ret;
+	}
+
+	return 0;
+}
+
+int reset_get_by_name(struct udevice *dev, const char *name,
+		     struct reset_ctl *reset_ctl)
+{
+	int index;
+
+	debug("%s(dev=%p, name=%s, reset_ctl=%p)\n", __func__, dev, name,
+	      reset_ctl);
+
+	index = fdt_find_string(gd->fdt_blob, dev->of_offset, "reset-names",
+				name);
+	if (index < 0) {
+		debug("fdt_find_string() failed: %d\n", index);
+		return index;
+	}
+
+	return reset_get_by_index(dev, index, reset_ctl);
+}
+
+int reset_free(struct reset_ctl *reset_ctl)
+{
+	struct reset_ops *ops = reset_dev_ops(reset_ctl->dev);
+
+	debug("%s(reset_ctl=%p)\n", __func__, reset_ctl);
+
+	return ops->free(reset_ctl);
+}
+
+int reset_assert(struct reset_ctl *reset_ctl)
+{
+	struct reset_ops *ops = reset_dev_ops(reset_ctl->dev);
+
+	debug("%s(reset_ctl=%p)\n", __func__, reset_ctl);
+
+	return ops->rst_assert(reset_ctl);
+}
+
+int reset_deassert(struct reset_ctl *reset_ctl)
+{
+	struct reset_ops *ops = reset_dev_ops(reset_ctl->dev);
+
+	debug("%s(reset_ctl=%p)\n", __func__, reset_ctl);
+
+	return ops->rst_deassert(reset_ctl);
+}
+
+UCLASS_DRIVER(reset) = {
+	.id		= UCLASS_RESET,
+	.name		= "reset",
+};